A Slice head is an emo / depressed / insane person whom is addicted to cutting themselves. Calling someone a slice head is like calling them stupid or crazy.
(Literal use) Did you see those cuts on Isaacs arms? He's obviously a slice head
(Insult use) Logan: Hey dude did you see the emoji movie? It was sick.
A mix between a stoner and a pothead. A stonehead is a rare breed that is resulted from being a stoner with many pothead friends. A stonehead is usually aware of the name of what they smoke but not of what it is.
Julie can be such a stonehead sometimes. She's so unware of how good her stash is.